GEOGRAPHY FORM THREE NOTES

GEOGRAPHY FORM THREE NOTES

STRUCTURE OF THE

EARTH

Physical geography can be simply defined as the study of the structure of the Earth and the forces which affect it. These forces are categorized into two kinds: internal and external forces. Internal forces are forces which act within or beneath the Earths crust. These forces result into various Earth movements such as vertical and horizontal movements, vulcanicity and earthquakes. External forces are forces which act inside the earths surface and result into various geomorphic processes such as mass wasting and weathering. The earth is composed of inner and outer zones (layers). The outer layer of the earth comprises of the atmosphere, biosphere and hydrosphere, while the inner layer includes the crust, mantle and core

The Earth's Crust, The Mantle, The Core and their Respective Characteristics Concentric Zones of the Earth

Identify concentric zones of the earth The earth is composed of three internal, concentric layers of increasing densities. These layers are the crust, mantle and core. They are made up of different layers of rocks, with their densities increasing towards the centre of the earth. That is, densities of rocks that make up the earth increase as you move from the surface towards the interior

The Crust (Lithosphere)

This is the outermost part of the earth. It consists of silica and aluminium (sial). It forms the upper layer of the continent and is mostly composed of granite rocks. The layer below SIAL is called SIMA. This layer is made of silica and manganese. It is a layer of basaltic rocks which are denser and underlies the continental block to form the ocean floor.

The Mantle (Mesosphere)

This is the layer below the crust. It is composed of iron and manganese. It lies between the crust and the core. The layer which separates crust and mantle is called Mohorovic discontinuity. The mantle is made up of very dense and hot igneous rocks, found in semi liquid states. It extends downwards 2900 km and the temperature ranges between 5000?C and 7000?C. The density of the mantle is 3 ? 3.3 g/cm3. It is divided into two parts namely, the upper and lower mantle. The upper mantle is rigid and combines with the crust to form a layer called lithosphere. Below the upper mantle there is a layer called asthenosphere

The Core (Barysphere)

This is the innermost layer of the earth. It is composed of nickel and iron. Its diameter is approximately 2500 ? 2700 km and its temperature is around 5500?C. The average density of the barysphere is about 5.2 g/cm3. Most geographers believe that the core is divided into solid and liquid core. The total mass of the earth is about 5.976 x 1021 tonnes.

Structure of the Earth

The Variation in Density and Thickness of the Concentric Zones of The Earth's Crust

Account for the variation in density and thickness of the concentric zones of the earth's crust ROCKS

A rock is an aggregate of mineral particles found in soft, solid or unconsolidated state. The earths crust consists of rocks and rocks consist of a combination of different minerals. All minerals are formed from one or more of eight main elements. These are: oxygen, silicon, potassium, sodium, calcium, magnesium, iron and aluminium.

Rocks can be broadly categorized into three types. These are igneous rocks, sedimentary rocks and metamorphic rocks. These kinds of rocks are classified according to their origin, chemical composition and age.

The Characteristics of The Earth's Crust, The Mantle and The Core

Describe the characteristics of the earth's crust, the mantle and the core Variations in characteristics of the three interior zones of the earth are the result of temperature and pressure as they increases from the surface to the center of the earth.Factors which accounts for such variations includes: pressure on the underlying materials, weight of the underlying materials, radioactivity, magma movement and heat generated during the formation of the earth.

Types of Rocks of the Earth's Crust The Types of Rocks of the Earth's Crust

Identify types of rocks of the earth's crust Igneous rocks

These rocks are formed when molten rock cools and solidifies. All igneous rocks originate inside the earth where they are under great pressure. Igneous rocks do not occur in layers and they dont contain fossils which are the chemically-changed remains of ancient plants and animals embedded in rocks. These rocks solidify either within the earths crust and form intrusive features or outside the earths surface and form extrusive features.

Igneous rocks are formed when the molten magma is forced out from the upper mantle to the earths surface, where it cools and solidifies due to low temperature. Crystals form on cooling and the rocks are called crystalline rocks.

There are two main types of igneous rocks:

1. Plutonic: these have solidified deep in the crust and they are seen on the surface only after being exposed by prolonged erosion. 2. Volcanic: these have been poured on the earths surface where they are called lavas.

Characteristics of igneous rocks

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